Gas-disabled liquid-pumping apparatus

ABSTRACT

Improved liquid-pumping apparatus uses a pumping chamber having a residual volume many times larger than the displacement volume and includes an outlet valve which is disposed within the lowermost region of the residual volume and which is biased against outflow of fluid therethrough for fluid pressures below a selected value.

United States Patent inventor Robert F. Shaw 350 Parnassus Heights, SanFrancisco, Calif. 941 17 Appl. No. 882,489

Filed Dec. 5, 1969 Patented Nov. 16, 1971 GAS-DISABLED LIQUID-PUMPINGAPPARATUS 13 Claims, 6 Drawing Figs.

11.5. CI. 417/417, 417/476, 417/490 Int. Cl ..F04b 35/04, F04b 49/08,F04b 7/04 FieldofSearch 4l7/4l7,

[56] Reierences Cited UNITED STATES PATENTS 2,015,574 9/1935 Webb417/476 2,552,195 5/1951 Lopata 417/490 X 2,925,814 2/1960 Vibber et a].417/417 Primary ExaminerR0bert M. Walker Attomey-A. C Smith PULSE SOURCE85 O VARY PULSE/PUMP RATE TO CATHETER PATENTI-Illauv 1s |9Tl SHEET 1 OF3 igure LIQUID DISPLACED LIQUID PUHPED AS FUNCTION OF TRAPPED AIR ANDRELIEF PRESSURE VOLUME 0F TRAPPED AIR (UNITS 0F PISTON DISPL.)

N0 AIR TRAPPED igure 2 INVI'YNTOR.

ROBERT F. SHAW BY 6L SMLA ATTORNEY PATENTEnunv 16 I87! SHEET 2 OF 3 BIASPRESSU\RE ZATMOSj- +10PSIG J 22 +5PS|G 26 25 29 mmos. I I I 1 7 VOLUME0F TRAPPED GAS (UNITS 0F PISTON DISPL.)

Figure 3 FROM RESERVOIR AND DRIP CHAMBER TO CATHETER igure 6 INVI'YNTUR.

ROBERT F. SHAW ATTORNE Y PATENTEUunv 16 I97! 3. 620,650

SHEET 3 or 3 TO CATHETE ROBERT F. SHAW SW'RL ATTORNEY GAS-DISABLEDLIQUID-PUMPING APPARATUS BACKGROUND OF THE INVENTION Certain knownliquid-pumping devices have been specifically adapted for meteredadministration of liquids into the vein or artery of a patient. Thesepumping devices, however, are generally limited by the hazardousdisadvantage that gas or air as well as liquid can be pumped into thepatients vein or artery as, for example, when the bottle or other supplyof liquid is expended and the system fills with air. Frequentexamination of the pumping device and liquid supply are consequentlyrequired to avoid pumping air into a patients vascular system. Thisinherently hazardous procedure has thus been costly to use and has notprovided entirely satisfactory operating results.

SUMMARY OF THE INVENTION Accordingly, the pumping apparatus of thepresent invention for administering liquids by positive displacementinto the vascular system of a patient provides inherent protectionagainst administration of gas or air. The present pumping apparatusincludes a pumping chamber having a residual volume which is many timeslarger than the displacement volume and having a biased outlet valvedisposed in the lowermost region of the residual volume. The carefulselection of interrelated values for displacement volume, residualvolume and outlet valve bias pressure assures that the present pumpingapparatus becomes selectively disabled from pumping liquid in thepresence of a predetermined volume of gas or air enclosed within thepumping chamber.

DESCRIPTION OF THE DRAWING FIG. I is a pictorial representation of thepumping apparatus of the present invention;

FIG. 2 is a graph showing the relationship between the displaced liquid,the volume of trapped air in units of displacement volume and the biaspressure provided by the outlet valve in the pumping apparatus of FIG.1;

FIG. 3 is a graph showing the relationship between fluid pressure andthe volume of trapped gas in units of displacement volume duringoperation of the pumping apparatus of FIG. 1;

FIG. 4 is a sectional view of electromagnetically actuated piston-typepumping apparatus according to the present invention; and

FIG. 5 is a sectional view of a peristaltic or roller-type pumpingapparatus in accordance with the present invention;

FIG. 6 is a sectional view of mechanically actuated bellowstype pumpingapparatus according to the present invention.

DESCRIPTION OF THE PREFERRED EMBODIMENT Referring now to FIG. 1, thereis shown a simplified pictorial diagram of the pumping apparatus of thepresent invention. It is convenient to refer to the volume of thepumping chamber 9 in units of displacement volume of the piston 11.Accordingly, for the purpose of analysis herein the pumping chamber maybe considered to comprise one, two or more units of displacement volume13. The pumping chamber includes an outlet valve which is biased againstoutflow therethrough for fluid pressures below a selected value and aninlet means 17 which admits fluid into the chamber 9 below the pistonwhile the piston 11 is in its maximal position prior to a pumpingstroke. A reserve chamber 19 above the piston 11 is coupled to the inletmeans via port 21 and thus serves as a reservoir of liquid and as a trapfor air or gas bubbles, as later described herein. The piston 11 and theinlet means 17 cooperate to permit equilibration of pressures betweenthe pumping chamber 9 and the reserve chamber 19 between pumpingstrokes.

For the purposes of analysis, the performance of the system may beconsidered when the pumping chamber 9 has only one unit of displacementvolume 13 (i.e., that outlet valve 15 is disposed at level 12). In thisform, the downward movement of piston 11 by one unit of displacementvolume to its minimal position at level 12 produces potentiallyindefinitely large fluid pressure within the chamber and leaves noresidual volume within the chamber. This is ideally suited for efficientand accurate pumping of known volumes of fluid but unfortunately iscapable or pumping both liquid and gas or air contained within thechamber volume 13.

A different situation pertains however, when the pumping chamber isenlarged to contain significant residual volume. Under these conditions,in the presence of a mixture of liquid and gas, the quantity of fluidpumped will depend upon the bias pressure provided by the outlet valve15. Thus, as shown in the graph of FIG. 2, if no air is trapped withinchamber 9 then one-displacement volume 23 of liquid is pumped per pistonstroke, substantially independently of the fluid-pressure bias of theoutlet valve. However, when gas is trapped within the chamber, thevolume of liquid displaced from the chamber by each piston stroke isless than one displacement-volume; the actual volume being a function ofboth the volume of trapped gas and of the pressure bias provided by theoutlet valve, as shown in the graph of FIG. 2.

FIG. 2 illustrates that the liquid pumping apparatus will be disabledwhen the trapped gas volumes are 2, 2.5, 4 and 6 times the strokevolumes, when the bias pressures provided by the outlet valve 15 arerespectively l5, l0, 5 and 3 pounds per square inch (p.s.i.).

Since for fail safe operation of the present pumping apparatus inmedical applications it is desirable to assure that only liquid and notair trapped within chamber 9 can be pumped, it might be concluded thatthe bias pressure provided by the outlet valve should be set as high aspossible to assure that even small bubbles of air entrapped within fluidchamber 9 inactivate the pumping mechanism. However, from the graph ofFIG. 2, it is apparent that the higher the value selected for the biaspressure provided by the outlet valve, the greater the degradation ofpump accuracy and efflciency, when volumes of air or gas inadequate todisable the pumping apparatus are trapped within pumping chamber 9.Under these conditions, a portion of the piston stroke volume isrequired to compress the trapped air or gas in order to build up fluidpressure to a valve which will overcome the bias of outlet valve 15 andthereafter, only the remaining portion of piston stroke volume displacesfluid from chamber 9 through outlet valve 15. Thus, the bias pressureprovided by outlet valve 15 should be sufiiciently high to disable thepumping apparatus when a selected volume of gas is present within pumping chamber 9 and should not be any higher than so required becausesystem accuracy suffers.

There is a minimum value of bias pressure provided by outlet valve 15which must be exceeded, and that value is determined by the height abovethe outlet valve at which the fluid reservoir may possible be disposed.Since the present apparatus may be used with a bottle or other reservoirof liquid which may be hung above the patient, the resultant fluidpressure at outlet valve 15 must be overcome to avoid a continuousoutflow of liquid through the pumping chamber 9 and valve 15 betweenpumping strokes under the influence of such resultant fluid pressure. Itis extremely unlikely that a reservoir bottle may be disposed more than6 of 8 feet above outlet valve 15 (which corresponds to liquid pressureof approximately 3 to 4 pounds per square inch) and therefore about 3 to4 pounds per square inch is an acceptable minimum value of the biaspressure provided by the outlet valve for use in parental fluidadministration. In actual practice, a bias pressure of approximately 5pounds per square inch for this application is a well selected valuesince it provides a reasonable safety factor in operation even if valvesprings, or the like, which set the bias pressure tend to weaken or areinitially below design specifications.

Referring, then, to the graph of FIG. 3, there is shown a family ofcurves of fluid pressure within the pumping chamber 9 as a function ofthe number of units of gas or air trapped within the chamber 9 expressedin units of piston displacement volumes. The fluid pressure withinchamber 9 can never exceed the value of bias pressure provided by outletvalve 15.

For the reasons discussed above, the value of bias pressure shown on thegraph of FIG. 3 is 5 pounds per square inch (gauge pressure) aboveatmospheric pressure. Thus, from the graph of FIG. 3 it can be seen thatif a volume of gas equal to the piston displacement volume is trappedwithin pumping chamber 9, about one-quarter of the displacement volume22 will be occupied in compressing the gas to the outlet bias pressureand the volume pumped 26 will be about three-quarters of the pistondisplacement volume. If the volume of trapped gas is two times thepiston displacement volume, the pumped volume 25 will be about one-halfof the piston displacement volume. If the volume of trapped gas is threetimes the piston displacement volume, the pumped volume 29 will be aboutone-quarter of piston displacement volume. However, if the volume oftrapped gas is four times the piston displacement, then no part of thevolume is pumped. Under such conditions, the piston strike is used toincrease the fluid pressure within the chamber 9 up to, but notexceeding, the value of bias pressure provided by outlet valve 15. Thepumping apparatus of the present invention having an outlet valve biaspressure of 5 pounds per square inch gauge pressure and having a chambervolume I3, 24, 27, 28 of at least four times the unit displacementvolume therefore becomes disabled to pump fluid when the volume oftrapped gas or air within the chamber is about equal to the total volumeof chamber 9 (i.e., four times the piston displacement volume). Itshould be apparent, however, from the graphs of FIGS. 2 and 3 that othervalues of outlet valve bias pressure and displacement units of residualvolume may be used in pumping apparatus according to the presentinvention which becomes disabled to pump fluid in the presence of aselected volume of gas within the chamber. For fail safe operation,then, the present pumping apparatus may include a residual volume whichis at least about one additional unit of displacement volume greaterthan is minimally required for a unit of displacement volume to producefluid pressure (i.e., with gas present in chamber 9) approximately equalto the value of bias pressure provided by outlet valve 15. The outletvalve should be located in the lowermost region of the residual volume(With the chamber 9 substantially vertically aligned) to assure that theoutlet valve 15 is always disposed in the liquid phase of fluids withinthe chamber 9. If from practical considerations, a volume of gasapproximately equal to four units of displacement volume requires toolarge a residual volume in chamber 9 in order to avoid having thepresent apparatus pump air, then the bias pressure provided by outletvalve 15 may be increased. From the graphs of FIGS. 2 and 3, it shouldbe apparent that the volume of gas within chamber 9 which disables thepresent apparatus from pumping liquid decreases as the bias pressureprovided by outlet valve 15 increases.

Referring now to FIG. 4, there is shown a sectional view of adisposable, cartridge-type pump assembly according to the presentinvention. In this embodiment, the outer housing 61 includes a reservoiror bubble chamber 63, the chamber 65 containing the pump-actuator andreturn spring, the piston chamber 67 defining the displacement volume,the residualvolume chamber 69 and the chamber 71 containing the outletvalve assembly. These chambers are all disposed along the direction ofliquid flow through the pumping apparatus substantially in the ordernamed.

The piston 73 is a conventional flexible-skirted cupped piston whichmoves a very short distance (typically a few thousandths of an inch)down the length of the piston chamber 67 in response to electromagneticforce applied to the piston actuator. This actuator includes a plate 75of magnetic material which is attached to (and, ideally, encapsulatedin) a plastic or other nonmagnetic piston driver 77. This piston driver,which is coupled to the piston 73, is captivated within the outerhousing 61 and is held against stops 79 at the upper end of is travel byspring 81. The plate 75 and the piston driver 77 with the piston 73attached thereto are all urged downwardly by the electromagnet 83 whichis disposed about the housing 61 below plate 75 when the electromagnetis energized at a selected-repetition rate of electrical pulses fromsource 85.

Fluid flows into the top of bubble chamber 63 from the drip chamber 35and thence substantially axially through apertures 86 in the pistondriver 77 to the top of piston 73. Longitudinal ports cut into thecylinder wall of the outer housing 61 about the piston 73 in itsuppermost most position permit fluid to flow around the piston prior toa pumping stroke and into the pumping chamber 67, 69. As soon as thepiston 73 moves downward from its uppermost position, these ports areclosed off so that the volume of displaced fluid can only flow out ofthe pumping chamber during a pumping stroke through the outlet valveassembly 72. The lower chamber 71 of the outer housing may includesuitable means for "bleeding" trapped gas out of the pump chamberinitially upon placing the pumping apparatus in service. For example,the lowermost portion 78 of the housing may be axially or longitudinallyslidable and may be spring-biased upwardly against the stop 74. Thus,manually urging the housing portion 78 downward against the return forceprovided by spring 76 relieves the force of the outlet valve spring 72and permits air to "bleed through the outlet valve. Return spring 76positions the housing portion 78 against stop 74 when released, toassure reestablishment of the proper bias pressure provided by outletvalve 72.

Such design factors as displacement volume, residual volume 69 andoutflow bias pressure may be determined in the manner previouslydiscussed in connection with FIG. 1 and the graphs of FIGS. 2 and 3. Inaddition, the volume of chamber 63 may be chosen to be larger than thetotal volume of the pumping chamber to permit any gas trapped therein toescape back through ports 87 for harmless collection in chamber 63.Also, this chamber establishes an ample reservoir of liquid below dripchamber 35 to provide a reasonably long period of continuous normaloperation after the supply of liquid in reservoir 33 is depleted.

Referring now to FIG. 5 there is shown one embodiment of the presentpumping apparatus which uses peristaltic action to pump only liquid.This embodiment of the present apparatus includes a length of flexibletubing 31 which provides a fluid conduit from the reservoir 33 andconventional drip chamber 35 to the hollow needle or catheter 37positioned within a vein or artery of a patients body. The pump includesan anvil 39 positioned on one side of the tubing 31 and having a statorportion 41 and a valve body portion 43. A rotatable roller carrier orrotor 45 includes a plurality of arms 47, each supporting a roller 49 atthe end thereof for engaging and squeezing the tubing 31 closed againstthe stator 41. The angular separation of the arms 47 of rotor 45 isgreater than the angle subtended by the arcuate surface of the stator41. This assures that the chamber portion of the tubing 31 which extendsfrom the outlet valve 48 to the upper edge 50 of the stator 41 is ventedto fluid pressure from reservoir 33 before each pumping cycle. Thus, itshould be noted that rotation of rotor 45 by suitable means (e.g., avariable-speed spring-driven or battery operated motor) causes a roller47 to squeeze the tubing 31 and thereby displace the quantity of fluidcontained within only the length of tubing 31 which is disposed adjacentthe arcuate surface of the stator 41. The remaining length of tubing 31disposed between the lower edge 52 of stator 41 and the outlet valve 48serves as the residual volume of the pumping chamber formed by theentire length of tubing 31 from the upper edge 50 to the outlet valve48. This residual volume (or, more conveniently, this residual lengthwhere tubing 31 has a known internal diameter) may thus be selected bythe same design considerations previously discussed in connection withFIG. 1 and the graphs of FIGS 2 and 3. The value of outlet bias pressureis determined by the spring 54 which overcomes the resiliency of thetubing 31 and squeezes it closed against the valve body 43. Also, topermit convenient visual observation of the pumping rate, it isdesirable to select the displacement volume per pumping stroke toapproximately equal the volume of one drop of the liquid to be pumped(approximately 1/10 to l/SO c.c.) so that the drip rate as observed indrip chamber 35 may provide a quick indication of the volume of liquidbeing pumped per unit time.

In this and other practical embodiments of the present invention, sincethe pumping apparatus is designed to become disabled from pumping liquidin the presence of gas within the pumping chamber, it becomes necessaryto vent any gas that may become trapped in the chamber when the pump isinitially placed in service. One convenient procedure that may be usedis simply to disable the outlet valve 48 initially as by relieving thespring force which squeezes the tubing 31 closed) in order to allowliquid to fill the entire conduit from reservoir 33 to the catheter 37.For this purpose, a relief knob 56 which is springloaded toward theanvil 39 may be temporarily withdrawn from its normal position against astop 57 in order to relieve the spring force and thereby bleed the airout of the system. The relief knob 56 is spring-loaded against the stop57 to assure reestablishment of the proper setting of the outlet valve48 upon release of the relief knob 56 following completion of thebleeding" procedure. In addition, for pumping apparatus of substantiallyaxially symmetrical design such as shown in FIGS. 4 and 6, or the like,an additional fail safe feature may be conveniently provided in order toinhibit operation when the outlet bias valve is not properly seatedafter a bleeding procedure. Specifically, the portion of the outerhousing surrounding the outlet valve may include an unaligned guide keyor pin or generally be altered in exterior shape or dimensions when theoutlet bias valve is improperly reseated so that the pumping apparatuscannot be positioned in operating position with respect to thepump-actuating means, as shown, for example, in the embodiment of FIG. 4in which a reference base 66 is disposed in fixed, spaced relationshipto the top of coil 83.

Referring now to FIG. 6, there is shown a sectional view of anotherembodiment of a disposable, cartridge-type pumping apparatus accordingto the present invention. In this embodiment, the outer housing 91includes a pumping chamber 93 having flexible chamber walls 95. in thisembodiment, friction and wear associated with moving piston parts areeliminated and the pumping stroke may be provided by compressing thechamber, say in an axial or longitudinal direction to alter its volume.Suitable means such as a variable-speed, springdriven orbattery-operated motor may be used to develop the axial compressiveforce required to produce a minute decrease (typically, a fewthousandths of an inch) in the longitudinal dimension of the chamber 93.

The inlet means to the pumping chamber 93 includes a valve which closesat the start of a pumping cycle to assure that displaced liquid may onlybe expelled from the pumping chamber during a pumping cycle by passingthrough outlet valve 103. In this embodiment, the inlet valve includestwo valve faces 96 and 98 with an aperture 101 through the upper valveface into the bubble or reservoir chamber 105. Thus, in the position ofmaximum extension of the chamber 93 prior to a pumping stroke, the twovalve faces 96 and 98 are spaced apart to permit fluid to flow from theupper reservoir chamber 105 through aperture 101 and between the valvefaces into the pumping chamber 93. However, since one of the valve faces96 is mounted on the bellows-type walls of the outer housing 91 formovement with respect to the other valve face 98, the passage for fluidflow between these faces and through aperture 101 is closed off so thatthe volume of fluid displaced from chamber 93 during a pumping strokecan only flow out through outlet valve 103. The other design factorssuch as displacement volume, residual volume, and outflow bias pressuremay be determined in the manner previously discussed in connection withFIG. 1 and the graphs of FIGS. 2 and 3.

Therefore, the pumping apparatus of the present invention becomesdisabled to pump liquid in the presence of a selected volume of gas orair trapped within the pumping chamber. Pump apparatus of this type isthus ideally suited for positivedisplacement liquid infusionapplications in medicine where a high degree of safety and reliabilityis required to prevent injury or death from accidental injection of airinto the veins or arteries of a patient.

1 claim: 1. Liquid infusion apparatus for selectively pumping a systemin which gas may be present, the apparatus comprising: a pumping chamberfor enclosing a volume of fluid, and

having an outlet valve which is biased against outflow of fluidtherethrough for fluid pressures below a selected value, said outletvalve being disposed to remain in communication only with liquid in thechamber in the presence of gas therein; means communicating with saidchamber for decreasing the volume thereof by a selected displacementvolume during a liquid-displacement period which preserves a residualvolume of the chamber that is greater than said selected displacementvolume; and inlet means communicating with said chamber and adapted toreceive a supply of liquid at an ambient pressure which is below saidselected value, said inlet means permitting bidirectional fluid passagetherethrough into said chamber between liquid-displacement periods forsubstantially equalizing fluid pressure within the chamber to ambientpressure prior to a liquid-displacement period and preventing outflowtherethrough from said chamber during the liquid-displacement period. 2.Liquid infusion apparatus as in claim 1 wherein: the ratio of volume ofsaid pumping chamber to volume of said displacement volume is greaterthan the ratio of the value of said fluid pressure bias provided by saidoutlet valve plus atmospheric pressure to the value of said fluid biaspressure. 3. Liquid infusion apparatus as in claim 2 wherein: theselected value of fluid pressure bias provided by said outlet valve isgreater than 3 pounds per square inch gauge pressure. 4. Liquid infusionapparatus as in claim 2 wherein: said selected value of fluid pressurebias provided by said outlet valve is approximately 5 pounds per saidinch gauge pressure; and manipulatable outlet said residual volume ofthe chamber is at least approximately four times greater than saidselected displacement volume. 5. Liquid infusion apparatus as in claim 1comprising; means coupled to said chamber in the lowermost region of theresidual volume thereof adjacent to said outlet valve for releasing gasfrom said chamber to establish communication between liquid in saidchamber and said outlet valve. 6. Liquid infusion apparatus as in claim5 wherein: said means coupled to said chamber includes a manuallymanipulatable element which is manually movable from a normallyoperational position to a position which disables the outlet valve fromestablishing said selected value of fluid pressure bias; and resilientbiasing means coupled to said element for urging said element into saidnormally operational position following release thereof from manuallyapplied forces to provide fail safe reestablishment of said selectedvalue of fluid pressure. 7. Liquid infusion apparatus as in claim 5wherein: said means coupled to said chamber includes a manuallymanipulatable element which is manually movable from a normallyoperational position to a position which disables the outlet valve fromestablishing said selected value of fluid pressure bias, and furtherincludes means cooperating with said element for preventing normaloperational communication between the chamber and said means fordecreasing the volume thereof in response to said element beingimproperly positioned to establish said selected value of fluid pressurebias. 8. Liquid infusion apparatus as in claim 1 wherein:

said inlet means includes a reserve chamber having a port passingbetween said chamber and said reserve chamber and having a volumegreater than said residual volume, said port blocking outflow of fluidtherethrough from said chamber during said liquid-displacement period.

9. Liquid infusion apparatus as in claim 1 wherein:

said means communicating with said chamber includes a piston which formsa fluid-confining boundary of said chamber and which is longitudinallymovable within said chamber; and

said inlet means includes a fluid channel within the wall of the chamberpositioned with respect to said piston for passing fluid therethroughinto said chamber while said piston is disposed at a position along thepath of longitudinal movement prior to said liquid-displacement periodand for blocking fluid flow out of said chamber in response to movementof said piston along said path during said liquid-dsiplacement period.

10. Liquid infusion apparatus as in claim 9 wherein:

said means communicating with said chamber includes an element ofmagnetic material coupled to said piston and a source of magnetic fluxdisposed with respect to said element for repetitively altering theposition thereof and of the piston coupled thereto.

11. Liquid infusion apparatus as in claim 1 wherein:

said means communicating with said chamber includes extensible boundarywalls which define said chamber;

said inlet means includes an aperture through the upper wall into thechamber, valve means disposed about said aperture for permitting fluidflow therethrough into said chamber for a selected longitudinalextension of said sidewalls, and for preventing fluid flow therethroughduring decrease of the volume of said chamber in response to movement ofthe extensible sidewalls; and

actuating means coupled to said sidewalls for cyclically moving theextensible boundary walls between selected dimensions at a predeterminedrepetition rate.

12. Liquid infusion apparatus as in claim 1 wherein:

said chamber includes a selected length of resilient flexible tubinghaving an internal fluid-confining passage therethrough of substantiallyuniform cross section along the length thereof;

said means communicating with said chamber includes a rotatable actuatorhaving at least one element which is disposed with respect to saidtubing for squeezing the same to close the passage therethrough, andwhich is responsive to rotation of said rotatable actuator for alteringthe location of the squeeze of the tubing over a selected portion of thelength of said tubing between a first limit near a fluid inlet end tosaid internal passage and a second limit remote from the first limit;and

said outlet valve includes another actuator resiliently biased tosqueeze said tubing to close the passage therethrough at a locationalong the tubing remote from the fluid inlet end thereof and spaced fromsaid second limit by a distance greater than the distance along saidselected portion of the tubing between the first and second limits, saidother actuator squeezing said tubing thereby establishing said selectedvalue of fluid pressure bias.

13. Liquid infusion apparatus as in claim 12 wherein:

said rotatable actuator being disposed with respect to said tubing toprovide during a portion of the rotational cycle thereof an unclosedinternal passage through said tubing from the fluid-inlet end thereof tosaid other actuator, and thereafter to provide during another portion ofthe rotational cycle thereof a closure of the internal passage throughthe tubing at a location therealong with advances over said selectedportion of length from said first limit to said second limit in responseto rotation of said rotatable actuator.

I l l UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No.3,620,650 Dated November 16, 1971 Invent r( Robert F. Shaw It iscertified that error appears in the above-identified patent and thatsaid Letters Patent are hereby corrected as shown below:

Column 6, line 43, "said inch" should read square inch after "and"delete "manipulatable outlet" Signed and sealed this 24th day of June1975.

(55.41,) Attest:

C. I'IARSHALL DANN RUTH C. MASON Commissioner of Patents attestingOfficer and Trademarks

1. Liquid infusion apparatus for selectively pumping a system in whichgas may be present, the apparatus comprising: a pumping chamber forenclosing a volume of fluid, and having an outlet valve which is biasedagainst outflow of fluid therethrough for fluid pressures below aselected value, said outlet valve being disposed to remain incommunication only with liquid in the chamber in the presence of gastherein; means communicating with said chamber for decreasing the volumethereof by a selected displacement volume during a liquiddisplacementperiod which preserves a residual volume of the chamber that is greaterthan said selected displacement volume; and inlet means communicatingwith said chamber and adapted to receive a supply of liquid at anambient pressure which is below said selected value, said inlet meanspermitting bidirectional fluid passage therethrough into said chamberbetween liquid-displacement periods for substantially equalizing fluidpressure within the chamber to ambient pressure prior to aliquid-displacement period and preventing outflow therethrough from saidchamber during the liquiddisplacement period.
 2. Liquid infusionapparatus as in claim 1 wherein: the ratio of volume of said pumpingchamber to volume of said displacement volume is greater than the ratioof the value of said fluid pressure bias provided by said outlet valveplus atmospheric pressure to the value of said fluid bias pressure. 3.Liquid infusion apparatus as in claim 2 wherein: the selected value offluid pressure bias provided by said outlet valve is greater than 3pounds per square inch gauge pressure.
 4. Liquid infusion apparatus asin claim 2 wherein: said selected value of fluid pressure bias providedby said outlet valve is approximately 5 pounds per said inch gaugepressure; and manipulatable outlEt said residual volume of the chamberis at least approximately four times greater than said selecteddisplacement volume.
 5. Liquid infusion apparatus as in claim 1comprising: means coupled to said chamber in the lowermost region of theresidual volume thereof adjacent to said outlet valve for releasing gasfrom said chamber to establish communication between liquid in saidchamber and said outlet valve.
 6. Liquid infusion apparatus as in claim5 wherein: said means coupled to said chamber includes a manuallymanipulatable element which is manually movable from a normallyoperational position to a position which disables the outlet valve fromestablishing said selected value of fluid pressure bias; and resilientbiasing means coupled to said element for urging said element into saidnormally operational position following release thereof from manuallyapplied forces to provide fail safe reestablishment of said selectedvalue of fluid pressure.
 7. Liquid infusion apparatus as in claim 5wherein: said means coupled to said chamber includes a manuallymanipulatable element which is manually movable from a normallyoperational position to a position which disables the outlet valve fromestablishing said selected value of fluid pressure bias, and furtherincludes means cooperating with said element for preventing normaloperational communication between the chamber and said means fordecreasing the volume thereof in response to said element beingimproperly positioned to establish said selected value of fluid pressurebias.
 8. Liquid infusion apparatus as in claim 1 wherein: said inletmeans includes a reserve chamber having a port passing between saidchamber and said reserve chamber and having a volume greater than saidresidual volume, said port blocking outflow of fluid therethrough fromsaid chamber during said liquid-displacement period.
 9. Liquid infusionapparatus as in claim 1 wherein: said means communicating with saidchamber includes a piston which forms a fluid-confining boundary of saidchamber and which is longitudinally movable within said chamber; andsaid inlet means includes a fluid channel within the wall of the chamberpositioned with respect to said piston for passing fluid therethroughinto said chamber while said piston is disposed at a position along thepath of longitudinal movement prior to said liquid-displacement periodand for blocking fluid flow out of said chamber in response to movementof said piston along said path during said liquid-dsiplacement period.10. Liquid infusion apparatus as in claim 9 wherein: said meanscommunicating with said chamber includes an element of magnetic materialcoupled to said piston and a source of magnetic flux disposed withrespect to said element for repetitively altering the position thereofand of the piston coupled thereto.
 11. Liquid infusion apparatus as inclaim 1 wherein: said means communicating with said chamber includesextensible boundary walls which define said chamber; said inlet meansincludes an aperture through the upper wall into the chamber, valvemeans disposed about said aperture for permitting fluid flowtherethrough into said chamber for a selected longitudinal extension ofsaid sidewalls, and for preventing fluid flow therethrough duringdecrease of the volume of said chamber in response to movement of theextensible sidewalls; and actuating means coupled to said sidewalls forcyclically moving the extensible boundary walls between selecteddimensions at a predetermined repetition rate.
 12. Liquid infusionapparatus as in claim 1 wherein: said chamber includes a selected lengthof resilient flexible tubing having an internal fluid-confining passagetherethrough of substantially uniform cross section along the lengththereof; said means communicating with said chamber includes a rotatableactuator having at least one element which is disposed with respect tosaid tubing for squeezing the saMe to close the passage therethrough,and which is responsive to rotation of said rotatable actuator foraltering the location of the squeeze of the tubing over a selectedportion of the length of said tubing between a first limit near a fluidinlet end to said internal passage and a second limit remote from thefirst limit; and said outlet valve includes another actuator resilientlybiased to squeeze said tubing to close the passage therethrough at alocation along the tubing remote from the fluid inlet end thereof andspaced from said second limit by a distance greater than the distancealong said selected portion of the tubing between the first and secondlimits, said other actuator squeezing said tubing thereby establishingsaid selected value of fluid pressure bias.
 13. Liquid infusionapparatus as in claim 12 wherein: said rotatable actuator being disposedwith respect to said tubing to provide during a portion of therotational cycle thereof an unclosed internal passage through saidtubing from the fluid-inlet end thereof to said other actuator, andthereafter to provide during another portion of the rotational cyclethereof a closure of the internal passage through the tubing at alocation therealong with advances over said selected portion of lengthfrom said first limit to said second limit in response to rotation ofsaid rotatable actuator.